Alice, Mathai; Dr.Nandakumar, C G(Cochin University of Science & Technology, November , 2004)
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Abstract:
Submarine hull structure is a watertight envelope, under hydrostatic pressure
when in operation. Stiffened cylindrical shells constitute the major portion of these
submarine hulls and these thin shells under compression are susceptible to buckling
failure. Normally loss of stability occurs at the limit point rather than at the
bifurcation point and the stability analysis has to consider the change in geometry at
each load step. Hence geometric nonlinear analysis of the shell forms becomes. a
necessity. External hydrostatic pressure will follow the deformed configuration of the
shell and hence follower force effect has to be accounted for.
Computer codes have been developed based on all-cubic axisymmetric
cylindrical shell finite element and discrete ring stiffener element for linear elastic,
linear buckling and geometric nonIinear analysis of stiffened cylindrical shells. These
analysis programs have the capability to treat hydrostatic pressure as a radial load
and as a follower force.
Analytical investigations are carried out on two attack submarine cylindrical
hull models besides standard benchmark problems. In each case, the analysis has
been carried out for interstiffener, interdeepframe and interbulkhead configurations.
The shell stiffener attachment in each of this configuration has been represented by
the simply supported-simply supported, clamped-clamped and fixed-fixed boundary
conditions in this study.
The results of the analytical investigations have been discussed and the
observations and conclusions are described. Rotation restraint at the ends is
influential for interstiffener and interbulkhead configurations and the significance of
axial restraint becomes predominant in the interbulkhead configuration. The follower
force effect of hydrostatic pressure is not significant in interstiffener and
interdeepframe configurations where as it has very high detrimental effect on
buckling pressure on interbulkhead configuration. The geometric nonlinear
interbulkhead analysis incorporating follower force effect gives the critical value of
buckling pressure and this analysis is recommended for the determination of collapse
pressure of stiffened cylindrical submarine shells.
Description:
Dept.of Ship Technology,Cochin University of Science & Technology